During the late 1930s, the Union Pacific often used helpers to move trains from Ogden to Wahsatch. The UP wanted to simplify this move so they asked their "Department of Research and Mechanical Standards" (DoRMS) to design a locomotive that could pull a 3600 ton train unassisted over the 1.14% grade of the Wahsatch.
The designers determined that to pull a 3600 ton train, a tractive effort of 135,000 lbs would be needed. Assuming a factor of adhesion of 4.0, the weight on drivers would have to be 4.0 * 135,000 = 540,000 lbs. Given an axle loading of 67,500 lbs each, this would require 8 drivers or an x-8-8-x wheel arrangement. The designers agreed upon the 4-8-8-4 design. Next, the horsepower and cylinder sizes were computed based on 300 psi boiler pressure. Although they weren't planning to pull these freight trains at 80 MPH, the DoRMS designed them for 80 MPH in order to have a sufficient factor of safety built into the design. What resulted is considered by many to be the most successful articulated steam locomotive ever built. Number 4000 was delivered to Omaha at 6PM, September 5, 1941.
The 25 Big Boys were built in two groups. The first group of 20 locomotives, called "Class 1", were built starting in 1941. They were numbered 4000-4019. The second group of 5 locomotives, "Class 2", were built in 1944. They were numbered 4020-4024.
The last revenue freight pulled by a Big Boy was in July of 1959. Most were retired in 1961. The last one was retired in July of 1962. As late as September, 1962, there were still four operational Big Boys at Green River, WY.
The total mileage of each of the Big Boys from class 1 were roughly the same
- 1,000,000 miles. 4016 had the lowest mileage -- 1,016,124. 4006 had the
highest mileage - 1,064,625. Of the second group, 4024 had the highest
mileage - 811,956.
NOTE: Some used "4-8-8-4 1" and "4-8-8-4 2" to distinguish between the first and second classes of Big Boys.
68: 68 inch drivers
23 3/4 - 23 3/4: Cylinder diameters (front and rear)
32: Piston stroke
540: 540,000 pounds of weight on drivers
MB: MB type stoker
|Usage Per 4 Hours||Usage Per Hour||Hours Per Full Tender||Miles Per Full Tender (at 25 mph)|
|Coal:||20 tons||5 tons||5.6||140|
|Water:||12,500 gallons||3125 gallons||8||200|
As you can see, coal was the limiting factor for the Big Boys. When working hard, a Big Boy could theoretically operation for over 5 hours and travel up to 140 miles. However, few enginemen would operate on low fuel (or water). It would have been common to refuel and take on water every couple hours or when convenient.
If one was to restore a Big Boy it would seem to make sense to start with the Big Boy that is in the best condition. At one time, this would have been 4023, currently at Kenefick Park, Omaha, NE. During the end of their careers both Challenger 3985 and Big Boy 4023 were rebuilt and placed in the Cheyenne UP roundhouse. However, 4023 was later placed on display in Omaha and the weather and environment has taken its toll on 4023. 4014, the Big Boy displayed for a long time in Pomona, CA had been kept in immaculate condition by the Southern California Chapter of the Railway & Locomotive Historical Society. Of all of the Big Boys that I had seen, 4014 looked to be in the best shape. I had thought that this would be the best restorationi candidate if a restoration were to ever happen.
According to many sources, the UP was never interested in running a coal-fired locomotive on their road any longer (the 3985 (4-6-6-4) was converted to oil in the late 1980's). Naturally, the next question one asks is "why not convert a Big Boy to burn oil?". This had been tried back in the 1940s or 1950s on 4005 with a single burner, without success. It had been said that it is not feasible to fire a Big Boy with oil due to the nature of the firebox (which was designed for burning semi-bituminous coal from southern Wyoming) and boiler capacity. However, 3985 was converted to burn oil and its firebox is not all that different from that of the Big Boy's.
Steve Lee (head of UP's steam program) had also stated that it wouldn't make much sense for UP to restore a Big Boy, as there were only two places on the entire system that are large enough to turn a Big Boy, and those places are only a few miles apart. However, the Challenger was often turned using wyes which could also, almost certainly, handle a Big Boy.
Data from tables and diagrams in 1947 Locomotive Cyclopedia and UP 11 - 1946 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. See also Henry B Comstock, The Iron Horse (New York: Galahad Books, 1971); "Union Pacific Gets Heaviest Articulated Locomotives", Railway Age, Volume 111, No 14 (4 October 1941), pp. 519-526, 528; and Wes Barris, "Centipede Tenders" on his steamlocomotive.com website at http://steamlocomotive.com/types/tenders/, last accessed 12 April 2020.(inter alia) Steam Update articles on "Steam Update: Big Boy's Cylinders Undergo `Boring' Process" at  and "Big Boy's New Suspension System Promises a Smooth Ride" at https://www.up.com/aboutup/community/inside_track/october-steam-update-10-31-2018.htm, last accessed 20 July 2019. (Many thanks to Kenneth Mileski for his 11 May 2016 email suggesting that Locobase's entry include information on 4014's restoration. Thanks as well to Chris Hohl for his 15 June 2019 email noting the 4014's cylinder diameter increase.) Works numbers were 69571-69575 in September 1941, 69576-69581 in October, 69582-69583 in November, 69584-69587 in December, 69588-69590 in January 1942. Union Pacific senior manager of Heritage Operations Ed Dickens Jr. said in 2016 that the 4-8-8-4 series originally was to have been called "Wasatch". After a never-identified UP worker wrote "Big Boy" on one of the cylinders, that nickname stuck. Firebox heating surface included 111 sq ft (10.3 sq m) in seven inverted-T shape circulators and a combustion chamber extending 9 ft 3 in (2.8 m) forward of the ashpan. One of the heaviest engines in the world, the 25 "Big Boys" were the largest steam engines ever built for regular service. The last five delivered in 1944 were fitted with Type A superheaters; see Locobase 13026 for an analysis of why the change was made. The Big Boys carried almost 70,000 lb (31,752 kg) more on its relatively tall drivers than did any other engine of comparable driver size. (The DM&IR's M3 2-8-8-4 engines -- Locobase 2405 -- had a higher weight on drivers, but had 63-inch/1,600 mm drivers.) Henry Comstock's back end paper illustration was dedicated to an exploded drawing of the Big Boy and included the comment:"That it could thunder safely over undulating and curved track at speeds inexcess of 70 miles per hour was due in large measure to two long-forgotten pioneers [Joseph Harrison and Anatole Mallet]." Ed Dickens, head of the Union Pacific Steam Team, described the front suspension that contributed to that success: "Leaf springs consist of special alloy spring steel metal plates clamped together. The steel plates are joined at the center with a heavy-duty spring buckle. The whole thing rests on spring saddles, giant castings that take the locomotive's weight and transfer it onto each wheel or driver. "In between the spring saddle on the bottom of the spring buckle is a pin," Dickens said. "The leaf springs teeter-totter up and down as necessary to respond to variations in track." The teetering movement allows the spring rigging to work as an interconnected system, constantly equalizing the locomotive's weight in response to the track. A double set of inner and outer coil springs - called a deadhanger point -- is located at the end of the locomotive frame to help absorb sudden shocks, or unexpected bumps. "The end has to be rigid, so the coil springs work nicely," Dickens said. Each one cost $265,000 when delivered. These engines could maintain 70 mph (113 km/h) and rode quite steadily; see Locobase 338 for a description of the revised bearing design that permitted smooth riding at such speeds.. (The four pistons evacuated 22,700 cu ft/642.8 cu m of steam per minute at that speed.) On the other hand, Farrington (1976) claims they were hard to fire and thought a feedwater heater should have been preferred to the exhaust steam injector they carried. Over a ruling grade of 1.14%, the 4-8-8-4s could move 4,000 tons (3,636 tonnes) of freight at 20-25 mph (32-40.25 km/h). When the ruling grade between Ogden, Utah and Green River, Wyoming (176 miles/283 km) was reduced to 0.82%, the tonnage rating climbed to 5,360 tons (4,873 tonnes). At 45 mph (72.5 km/h), these engines developed 6,000 drawbar horsepower (4,476 kW). Among their many abilities was the flexibility to move around curves of 20 deg. Also, the online encyclopedia  (visited 14 July 2005) notes approvingly: "They did sterling service in the Second World War, especially since they proved so easy to fire that even a novice could do a fair job. Since many men who were unsuited to combat service were instead drafted into railroad service to replace crewmen who joined up, this proved essential." See the trainorders.com forum thread that began 1/05/2013 () when KeyRouteKen commented on a recent documentary: "One of the guys talked about shoveling 27 tons of coal "by hand". Stoker must have been inoperable. Then he said they dropped down one time to 165 lbs of steam so they threw some creosoted pieces of crossties in the firebox to raise steam again. That was funny. "And the best story was the guy who would open the firebox door and hold his shovel there to make a vent. Great, except when the hogger pulled back on the throttle, and the entire shovel was sucked into the firebox ! (grin!) " Bob3985 replied:"The fireman who hand fired the Big Boy was Dillard Hill and they indeed had broken the stoker auger and could not auto deliver the coal to the firebox so they set their train out and made a run for the Laramie roundhouse keeping the steam up by hand." Hotwater added:"... hand firing any locomotive equipped with a stoker, it really isn't THAT big of a deal. Just because the stoker auger doesn't work, does NOT mean that the steam distributing table doesn't function. All that is needed is for one or two men (Fireman & Headend Brakeman) to continuously shovel the coal onto the distributing table, and the steam jets will blow the coal to the necessary portions of the firebox. I speak from experience! It works on any steam locomotive equipped with a stoker." 4005 was converted to oil-firing for trials in 1945. Within a year, she was converted back to coal firing and no other Big Boys were converted. According to Chris Hohl, 4019 was fitted with smoke deflectors for tests in 1944-1945; no other members of the class were converted. Drawing from William Kratville's book Big Boy, Nick Chillianis posted information about tests conducted 3 April 1943 on the Wasatch grade. Wes Barris's tender entry notes that hauling a 3,600 ton train nonstop from Ogden to Echo--40 miles/64.4 km--required virtually all of the tender's capacity of coal and water. Pushed at a rate of 9,980 US gallons (37,434 litres) of water and 9.66 tons (8.8 tonnes) of coal consumed per hour, engine #4016 produced 7,157 hp (5,339 kW) at the cylinders while moving 3,883 tons (3,530 tonnes) of train at 41.1 mph/66 km/h (drawbar hp was 6,290.) Other engines in the test produced 5,800 dbhp (4,327 kW) under similar conditions. See  (12 Nov 1998, 8:46 AM). At Ken Mileski's suggestion, Locobase checked up on 4014's restoration to service. In July 2013, the Union Pacific struck an agreement with the Southern California Chapter of the Railway & Locomotive Historical Society in Pomona, Calif to regain ownership of the 4014, which had been on display at the Rail Giants Train Museum since 8 January 1962. According to the UP, 4014 had run 1,031,205 miles in less than 18 years of service before its final revenue run on 21 July 1959. (That computes to a daily average of 160 miles for every calendar day.) In exchange, UP transferred title of UP 6-axle diesel SD-40-2 #3105, a boxcar, and a caboose. After months of careful assessment and preparation, four UP diesels moved the 4014 onto the national rail network on 26 January 2014. Ten freight cars provided additional braking power. Its first stop was Colton, CA, where it remained until its 1,300 mile (2,093 km) journey to Cheyenne, WY. That trip ended on 8 May 2014 with the 4014's safe arrival. An initial estimate of 3-5 years for the restoration was later revised to 5-7 in part because the steam shop at Cheyenne had to be substantially modified to accommodate 4014. In addition, many systems, such as the entire front engine, were removed to allow better access during their reconstruction. The project's coverage included details on some of the design features that contributed to the 4000' class's success. One significant change was the conversion to oil fuel (#5 fuel oil) from coal burning. Jim Wrinn confirmed to Chris Hohl that boring the cylinders in the 4014 had increased their diameter to 24" (610 mm) during the restoration, which raised the initial tractive effort to 138,240 lb (67,205 kg or 614.9 kN). At just under 350 tons (316.3 tonnes), the 4014 is the largest wheeled restoration project ever undertaken. As almost every steam railfan knows, the UP met the five-year goal by conducting a test run on 2 May 2019 and delivering the Big Boy to Cheyenne on 8 May 2019.
Data from UP 11 - 1946 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Rail Data Exchange. (Thanks to Chris Hohl for his email correcting the driving wheelbase.) Works numbers were 72777-72781 in November 1944.Locobase 346 describes the first twenty of these Big Boys. This later quintet is usually described as reflecting the wartime limitations of certain metals, which required the builder to substitute heavier steel components. Even so, their engine weights were still lower than the maximum weights believed to have afflicted the C & O's 2-6-6-6 H-6 Allegheny class (Locobase 304). Firebox heating surface included 111 sq ft (10.3 sq m) in seven inverted-T shape circulators and a combustion chamber extending 9 ft 3 in (2.8 m) forward of the ashpan. What is not usually mentioned is the change in boiler heating surface area and the substitution of a Type A superheater for the earlier group's Type E. John E. Rimmasch of Wasatch Railroad Contractors contributed to a Trainorders forum discussion with comments that shed light on the reason for the change (): On May 25, 2011, Rimmasch lays out the conditions that most likely dictated the change: "On the UP between 1941 and the end of steam, it was not uncommon to see super power get new tubes annually or even every six months. This was due in large to a number of conditions. A.) The water in Utah and Wyoming was hard enough that the flue bundle would clog up and tubes would burn quickly. B.) The UP Super Power was high pressure steam, which means we had a lot more heat. 800's, 300 psi, Big Boy's 300 psi and Challengers 280 psi. C.) The length of the tubes in the 800s, 3900s and 4000 was nearly the maximum allowable tube length for any locomotive (respectively 20-22 feet [6.1-6.7 m] long). It was found that when tube lengths near or surpass 18 feet long [5.5 m] , they had more of a tendency to bounce and tear apart. The stretching effect on these long tubes precluded many of them from being re-used. "In the case of the UP, when you combine all three symptoms above, you end up having to change tubes more often ... [R]ather than lose a locomotive on tube failure, the UP (and other lines) found it cheaper and better to simply change them more frequently. ...A Big Boy could get new tubes in less than 36 hours." In a later post, Rimmasch argues that Alco used a Type E superheater, which was harder to maintain because of its more complex steam path, to cover its bets: "I assume that the Big Boy originally had type E's with an increased heating surface area as ALCO was unsure if they had produced enough heating surface area to support the bore and stroke (multiplied by 4) and, after delivery quickly found that they had enough steaming capacity that the locomotive did not require type E's and was therefore reduced to type A's." Rimmasch implies that the change to Type A superheaters came during the production of the first twenty locomotives, but the 1946 diagrams show only that the 4884-1s had Type E and the 4884-2s had Type As. Like the earlier batch, these engines served the UP into the 1960s before all of them were retired in 1962--4021 in January, 4022 in February, and 4020, 4023-4024 in July.
|Principal Dimensions by Steve Llanso of Sweat House Media|
|Class||Big Boy (4884-1)||Big Boy (4884-2)|
|Railroad||Union Pacific (UP)||Union Pacific (UP)|
|Number in Class||20||5|
|Locomotive Length and Weight|
|Driver Wheelbase (ft / m)||36.50 / 11.13||36.50 / 11.43|
|Engine Wheelbase (ft / m)||72.45 / 22.08||72.46 / 22.09|
|Ratio of driving wheelbase to overall engine wheebase||0.50||0.50|
|Overall Wheelbase (engine & tender) (ft / m)||117.58 / 35.84||117.58 / 35.84|
|Axle Loading (Maximum Weight per Axle) (lbs / kg)||67,800 / 30,754||67,800 / 30,754|
|Weight on Drivers (lbs / kg)||540,000 / 244,940||545,200 / 247,299|
|Engine Weight (lbs / kg)||762,000 / 345,638||772,250 / 350,287|
|Tender Loaded Weight (lbs / kg)||427,500 / 193,911||436,500 / 197,993|
|Total Engine and Tender Weight (lbs / kg)||1,189,500 / 539,549||1,208,750 / 548,280|
|Tender Water Capacity (gals / ML)||24,000 / 90.91||25,000 / 94.70|
|Tender Fuel Capacity (oil/coal) (gals/tons / Liters/MT)||28 / 26||28 / 26|
|Minimum weight of rail (calculated) (lb/yd / kg/m)||113 / 56.50||114 / 57|
|Geometry Relating to Tractive Effort|
|Driver Diameter (in / mm)||68 / 1727||68 / 1727|
|Boiler Pressure (psi / kPa)||300 / 20.70||300 / 20.70|
|High Pressure Cylinders (dia x stroke) (in / mm)||23.75" x 32" / 610x813 (4)||23.75" x 32" / 603x813 (4)|
|Tractive Effort (lbs / kg)||135,375 / 61405.14||135,375 / 61405.14|
|Factor of Adhesion (Weight on Drivers/Tractive Effort)||3.99||4.03|
|Tubes (number - dia) (in / mm)||75 - 2.25" / 57||212 - 2.25" / 57|
|Flues (number - dia) (in / mm)||184 - 4" / 102||73 - 5.5" / 140|
|Flue/Tube length (ft / m)||22 / 6.71||22 / 6.71|
|Firebox Area (sq ft / m2)||704 / 65.40||720 / 66.89|
|Grate Area (sq ft / m2)||150.30 / 13.96||150 / 13.94|
|Evaporative Heating Surface (sq ft / m2)||5889 / 547.10||5755 / 534.85|
|Superheating Surface (sq ft / m2)||2466 / 229.10||2043 / 189.87|
|Combined Heating Surface (sq ft / m2)||8355 / 776.20||7798 / 724.72|
|Evaporative Heating Surface/Cylinder Volume||179.43||175.35|
|Computations Relating to Power Output (More Information)|
|Robert LeMassena's Power Computation||45,090||45,000|
|Same as above plus superheater percentage||58,617||56,700|
|Same as above but substitute firebox area for grate area||274,560||272,160|
A later report stated that the boiler jacketing had been removed to prevent moisture entrapment. She had been painted recently. Her state of preservation included libricated bearings.
Today, 4018 has been repainted and cosmetically is looking much better.
4023 was then moved to Kenefick park where it sat for many
years next to Centennial DDA40X 6900.
The weather and environment had taken its toll on 4023.
In the early 2010s the city of Omaha decided to re-design the riverfront area including the old UP shops, local industries, and Kenefick park into a new convention center. 4023 was to be placed on display at the convention center site after construction was completed. However, a change in the convention center plans no longer include the display of 4023 and the DDA40X. The locomotives had been temporarily moved to the Durham Western Heritage Museum in downtown Omaha. In March of 2005, 4023 was moved to a location near the Lauritzen Gardens. 4023 is in good shape. The paint looks great and all the missing parts (headlight etc.) have been replaced.